1. Field of the Invention
The invention relates to a silicone composition useful for adhesively fixturing matably engageable structural elements, such as in threadlocking of bolt/nut assemblies, so that the structural elements are adhesively bonded and sealed upon their being engaged in a final interlocked state.
2. Description of the Related Art
It is common practice in the use of threaded mechanical fasteners such as screw/nut assemblies, bolt/nut assemblies, or the like, to apply to one or more of the threadable engagement surfaces thereof, an adhesive/sealant composition, termed a threadlocking composition, for the purpose of locking and sealing the constituent members of such fasteners when they are engaged in their final interlocked state.
Such threadlocking compositions significantly increase the torque required to break or turn the engaged threaded members. Of the many threadlocking formulations known in the art, one of the most popular compositions is a co-reactive adhesive system. With this type of threadlocking system, two or more ingredients are mixed before applying the resulting composition to the threadable engagement surface(s) of the fastener on which the components in the threadlocking composition react to cure. Examples include epoxy adhesive resin formulations.
Other threadlocking formulations include reactive monomer threadlocking compositions typically comprising a monomer and a polymerization initiator of the monomer. Often it is useful to microencapsulate the monomer. U.S. Pat. No. 5,397,812 discloses a threadlocker composition in which micro-capsules enclose at least a reactive monomer of a reactive adhesive composition comprising the monomer, a polymerization initiator for the monomer, and an activator of the polymerization initiator, and are dispersed in a binder comprising a photo-hardenable resin composition. The binder composition may comprise a photoinitiator such as an onium salt, for curing thereof by suitable radiation such as ultraviolet radiation.
U.S. Pat. No. 4,417,028 describes a co-reactive system including a polymerizable monomer; an initiator, a polymerization accelerator, and a binder, in which the initiator, e.g., peroxide initator, is microencapsulated.
U.S. Pat. No. 4,035,355 discloses compositions containing acrylate-containing polyorganosiloxane reactive monomers, but neither peroxides or micro-encapsulated initiators are described.
Other co-reactive systems also exist but all have serious disadvantages such as low heat resistance, inferior strength, and poor oil tolerance. Further, the use of such compositions generally requires that the threaded members be degreased with an organic solvent before engaging the members or applying the adhesive in order to ensure adequate bonding.
Regardless of the specific formulation, the threadlocking formulation is desirably paste-like in consistency with sufficient viscosity and sag-resistance to permit ready application of the composition to the threads of the threadably matable fasteners, without subsequent dripping, sagging or displacement of the composition from the threads prior to mating and threadably locking the mechanical fastener components. Once applied to the threaded fastener, the threadlocking formulation remains on the threaded surface until the fastener is used. In use, the fastener with the preapplied threadlocking formulation thereon is contacted with mating surface or structure, e.g., a complementarily threaded engagement member, which may additionally have the threadlocking formulation previously applied to the engagement surface thereof, to facilitate the fixation of the engaged parts. In such manner, a differential pressure is applied to the matably engaged elements.
As the element bearing the threadlocking formulation is brought into engagement with complementary mating structure, the locus of engagement, which includes the previously applied threadlocking formulation, is restricted from access to the open air environment. Threadlocking formulations have therefore utilized various anaerobic curing adhesive compositions, due to the rapid curability of such compositions in the substantial absence of oxygen.
It would be extremely useful and a significant advance in the field of co-reactive threadlockers and sealants, and accordingly is an object of the present invention, to provide a reactive formulation useful for threadlocking applications, which overcomes the disadvantages of the prior art compositions.